A local farmer asked me to help him out with his farm truck. Its a 1999 Ram 1500 4x4 Auto with a 5.2L (318). The issue that the farmer is having is that the truck will start but wont stay running. A local shop replaced the fuel pump on it but that wasnt the issue. The fuel pump works, the relay works for it and you can hear the pump kick on. Fuel is getting to the fuel rail up on the engine and as long as you press the gas pedal down the engine stays running. As soon as you let off the gas pedal the engine sputters and shuts off. I took some starting fluid to it and the starting fluid didnt help at all as soon as you let off the pedal the truck doesnt idle it just shuts off. The truck doesnt idle at all actually, once you start cranking and the engine starts if the gas pedal isnt depressed the engine shuts off. I have had 4.6 and 5.4 V8 Ford Engines run like that if they werent getting enough air or if the Mass Air Flow sensor was bad so I took the throttle body off and cleaned all the dirt and grime out of it. I removed the Idle Air Control Valve and it was covered in solid carbon and dirt same as the Mass Air Flow Sensor. I removed the vacuum fitting from the MAF sensor that connects to the Throttle Body and found that the MAF was full of dirt. I have ordered a new MAF and IAC as they are the originals from 1999. Would either of those sensors cause the truck to run like its doing ? The IAC has 12 volts on two of its pins and the other two have ground. The mass air flow also has power and ground across its three pins. Electrically they are getting supplied the power they need. There are no codes set or stored and no CEL on. If anyone has any other ideas at how to fix this issue Im all ears. I see a lot of internet posts about issues similar to this with no solutions found. Thanks ahead of time to all who reply.

 

Start with cleaning the throttle body, paying particular attention to the IAC well. Remove the IAC, clean it out really well. Disconnect the battery before you start, hook it back up when you have it back together. Then, turn the ignition to 'on', not start, count to ten, don't touch anything. THEN start the truck. If everything is working as it should, it'll figger out idle pretty quick.

 

Does a faulty IAC valve usually cause these trucks to act like this ? I ordered a new one since the old one is 25 years old.

 

I would try the cleaning first. Generally, if one fails, the PCM will whine about it. That, and the aftermarket fellers don't always play nice with these trucks...... I have had zero success with them.

 

aren't helping much with just a voltmeter and no scan tool.
If his 1999 5.2 Ram has a MAF that's the first I've heard, they use speed density to calculate incoming air: RPM, MAP, and internal memory table.
If you mean MAP, a scantool should show it at atmospheric pressure engine off (29.92Hg) and 12-18 at idle. Yes to clogged MAP will stall the engine.
IAC can be tested by going to IAC test and adjusting idle RPM, if RPM doesn't change the IAC is stuck.
Unlike IAC on other vehicles, it doesn't have a sensor to detect pintle position so won't throw a code if it won't move to the position the PCM commands it. The Ram's IAC code is a basic driver circuit test to see if there are shorts.

 

I have a Snap On Solus Ultra I just didnt have it on me at the time. Dont gotta be cocky.

 

I've had cleaning the IAC resolve these sorts of issues on multiple occasions. I also had a bad battery cause these issues on one occasion. It didn't make sense to me but replaced the battery and all stalling issues were gone. The battery didn't appear to be faulty, it started the truck just fine. Maybe it was a result of resetting the computer having the cables unhooked.

 

Right there with ya on that one. My truck has always been hard to start, slow crank. Replaced the battery, didn't help. Replaced the starter, didn't help..... just lived with it for several years. Recently the truck started stalling on warm restart..... it was intermittent, but, kinda consistent... then, went out to go to work one day, and no start. Just clicks. Gave it a boost to start, drove it to work. (ten miles or so. about 20 minutes on the road) Wouldn't start after work either.... co-worker gave me a jump, drove directly to the battery store, had a new one installed. (holy SMOKES have those gotten expensive.....) New battery, truck cranks right up, no more slow cranking, and no more stalling either.....

 

Years ago my battery was old and having issues starting the truck. I got a used one from work that load tested better than the one i had. Worked for a short time but would start fine but wouldn't idle on it's own. Load tested the battery and it was in the weak zone. New battery and and no idle issues. So have the battery load tested before replacing the iac.

 

Update for the thread. I replaced the IAC and MAP sensor and the truck fired right up and ran fine. Took it for a spin and then it began misfiring. Pulled the spark plugs and found they were fouled up went ahead and changed them out and truck is good to go. Plugs got wet from all that cranking we did without the truck firing up I believe. Thanks everyone for all the advice.